Oracle Merge vs Select then Insert or Update

Question

What is faster?

the Merge statement

    MERGE INTO table_name 
     USING dual
     ON (row_id = \'some_id\')
    WHEN MATCHED THEN
     UPDATE SET col_n         


        

Answer 1

Take care of the merge. It can consume a lot of your area TEMP using HASH JOIN. Test him using hint FIRST_ROWS or use UPDATE view join plus INSERT with NOT EXISTS.